4 Answers
4

Glovis is one of the best places to start compiling free satellite imagery. For a new user, LANDSAT imagery is a great place to start - you will be able to find data covering the 1970's to present day. There is also a wealth of information available for working with this data. For example, if you are using ArcGIS you can quickly learn how to develop a landcover map. This page lists some free data viewers that you may find useful.

Earth Explorer would be a great place to look for satellite and aerial imagery along with data such as "Forest Carbon Sites". A really interesting project would be to look at canopy cover change over the last 30 years using Landsat imagery.